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Recently I ordered enough parts to assemble a 350L upper. My two 6.5 Grendels are not legal hunting Rifles in some states I visit. For assembly I had to buy every tool but a vice. I have a 6.5 upper with a 12 inch Group buy Green Mountain barrel from last year. My buddy put it together for me but barrel was not a tight fit in the Aero receiver, he did not shim it at assembly.. So now its my turn...I took it apart, barrel nut did have grease on it. I had some Stainless 0.001 shim stock and Locktite 620 on hand for this rebuild.. I first lapped a spare receiver and 2 other receivers with a Brownell tool. This went well, I made sure to keep the tool well oiled and kept grit out of receiver. Cleaned up the 3 receivers and tool and let them dry.. The Faxon 350 barrel was a snug fit but I used some 620 anyway. I installed the barrel nut with aeroshell grease, crow foot wrench on a breaker bar, snugged it and loosened it 3 times and then final tightened it a torq wrench at 50 ft lbs. After installing the gas block onto the dimpled barrel I realized I had left the port door off...This was my first time so I know there is a learning curve.. No problem, barrel nut off and got door installed and completed the assembly at 55 ft lbs.. It went well and was pretty easy..
The next day I got the 12 inch Grendel together. I checked the GM barrel and Aero upper with my Mitutoyo dial calipers. It looked like the upper was 0.0015 to 0.002 larger than the barrel extension. I used my good Fiskars shop scissors to cut the 0.001 shim material, shim covered 95% or more of the extension. fit was tight but I did lube it up with some of the 620 and got it in with some effort.. I wiped off excess 620, added more aeroshell grease to nut and receiver threads, torqed barrel nut...And a miracle happened...The nut to hand guard was timed perfect, I mean Perfect.. Last year the barrel nut tightened down to far and we had a hard time getting the 8 screws into the holes, they went in but with some difficulty....Right or wrong this time I added three 0.004 barrel shims to bring hole closer to center of hand guard holes, this worked, screws went right in. I had dimpled the barrel a few days earlier using a Kaw Valley dimpling jig. I got everything assembled including scope, QD and accessory mount for red or green light. I now need to shoot a few rounds and see if groups tightened up a little, there was no problem before but I did want to shim barrel and dimple the barrel. My rifles are for hunting with 99% of my shot less than 75 yards but I still like to have nice tight groups at 100 yards. These 2 uppers were fun and I look forward to assembling 2 more soon..
The next day I got the 12 inch Grendel together. I checked the GM barrel and Aero upper with my Mitutoyo dial calipers. It looked like the upper was 0.0015 to 0.002 larger than the barrel extension. I used my good Fiskars shop scissors to cut the 0.001 shim material, shim covered 95% or more of the extension. fit was tight but I did lube it up with some of the 620 and got it in with some effort.. I wiped off excess 620, added more aeroshell grease to nut and receiver threads, torqed barrel nut...And a miracle happened...The nut to hand guard was timed perfect, I mean Perfect.. Last year the barrel nut tightened down to far and we had a hard time getting the 8 screws into the holes, they went in but with some difficulty....Right or wrong this time I added three 0.004 barrel shims to bring hole closer to center of hand guard holes, this worked, screws went right in. I had dimpled the barrel a few days earlier using a Kaw Valley dimpling jig. I got everything assembled including scope, QD and accessory mount for red or green light. I now need to shoot a few rounds and see if groups tightened up a little, there was no problem before but I did want to shim barrel and dimple the barrel. My rifles are for hunting with 99% of my shot less than 75 yards but I still like to have nice tight groups at 100 yards. These 2 uppers were fun and I look forward to assembling 2 more soon..
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